Video signal processing device and method

ABSTRACT

A video signal-processing device that can improve the apparent contrast of the luminance signal at a television receiving set includes a quantity of black expansion computing section for computationally determining the quantity of black expansion when the luminance component of the input video signal is not higher than a first luminance level, a gain controller for regulating the quantity of black expansion as computationally determined by the quantity of black expansion computing section, a quantity of black expansion adding section for generating an output video signal by adding the quantity of black expansion regulated by the gain controller to the luminance component of the input video signals and a vertical span adding block for integrating the luminance component of the output video signal not higher than a second luminance level for a field. The gain controller regulates the quantity of black expansion according to the luminance component integrated by the vertical span adding block to improve the apparent contrast of the luminance signal at the television receiving set by accurately expanding black.

TECHNICAL FIELD

This invention relates to a device and a method for processing videosignals to be used for the purpose of improving the black contrast in atelevision receiving set or the like.

The present application claims priority from Japanese Patent ApplicationNo. 2002-185038 filed on Jun. 25, 2002, content of which is herebyincorporated by reference into this application.

BACKGROUND ART

The signal level of black color of video signals transmitted totelevision receiving sets for the purpose of displaying images on thedisplay screen of the television set can vary depending on thebroadcasting station, the TV camera, the type of the home use VTR or thelike. It is known that the apparent black contrast is improved byexpanding (the amplitudes of) signals for black in the televisionreceiving set that reproduces video signals. FIG. 1 of the accompanyingdrawings is a block diagram of a video signal-processing device 7proposed in Japanese Patent Application Laid-Open Publication No.7-154644, which is a typical black level expansion circuit.

The video signal-processing device 7 illustrated in FIG. 1 comprises aninput terminal 71, a black expanding section 72, an output terminal 73,a black peak holding section 74, a comparator 75, a pedestal leveltransmitting section 76 and a gain control amplifier 77. The videosignal-processing device 7 operates for feed back control in order tomake the peak position of the input black level (to be referred to asblack peak level hereinafter) agree with the pedestal level.

The black expanding section 72 performs an operation of black expansionon black level signals lower than a predetermined threshold level TH asshown in FIG. 2A out of the video signals input by way of the inputterminal 71 depending on the feedback gain input from the comparator 75.The black expanding section 72 then transmits the black level signalsthat have been subjected to an operation of black expansion to theoutput terminal 73 and the black peak holding section 74. The videosignals transmitted to the output terminal 73 are output to thetelevision receiving set without modification.

The black peak holding section 74 sequentially takes out only the videosignals that do not contain any synchronizing signal component out ofthe transmitted black level signals and detects the black peak level BLof each of the signals. The black peak holding section 74 applies thedetected black peak level to the comparator 75. The configuration of theblack peak holding section 74 will be described in greater detailhereinafter.

The comparator 75 receives the black peak level from the black peakholding section 74 and the pedestal level Ep as shown in FIG. 2B fromthe pedestal level transmitting section 76. Then, the comparator 75determines the difference between the black peak level and the pedestallevel Ep and outputs the difference to the gain control amplifier 77.

The gain control amplifier 77 generates a feedback gain on the basis ofthe black peak level and the pedestal level Ep input to it and transmitsthe feedback gain to the black expanding section 72. Note that the gaincontrol amplifier 77 generates a feedback gain so as to reduce thedifference between the black peak level and the pedestal level input toit. Upon receiving the feedback gain, the black expanding section 72 canperform an operation of black expansion so as to make the black peaklevel agree with the pedestal level Ep.

As the black expanding section 72 repeats the operation of transmittinga video signal that has been subjected to an operation of blackexpansion to the black peak holding section 74 for the black levelsignals, it is possible to make the black peak level gradually comeclose to the pedestal level Ep. Thus, the video signal-processing device7 can converge only the video signals with a black level lower than thepredetermined threshold level TH as shown in FIG. 2B to a constantluminance level and can hold the video signals other than black levelsignals without manipulating the amplitude so that it is possible toimprove the black contrast, while maintaining the brightness of theentire image to a constant level.

Now, the black peak holding section 74 of the video signal-processingdevice 7 will be described in greater detail. FIG. 3 is a schematiccircuit diagram of the black peak holding section 74. The black peakholding section 74 comprises an input section 81 for receiving videosignals that have been subjected to an operation of black expansion fromthe black expanding section 72, a first transistor 82, a secondtransistor 83, a third transistor 84, a first power source 86, a secondpower source 87, a resistor 88, a black area control resistor 89, acapacitor 90, an output section 91 for applying the detected black peaklevel to the comparator 75, a first current source 92 and a secondcurrent source 93.

The first transistor 82 receives the video signal Be that is expandedfor black from the input section 81 by way of its base terminal. Itsemitter terminal is connected to the first current source 92, while itscollector terminal is connected to the base terminal of the resistor 88and the base terminal of the third transistor 84. The second transistor83 has its base terminal connected to the second current source 93, thecapacitor 90, the output section 91 and so on and is adapted to transmitthe held black peak level to the comparator 75 by way of the outputsection 91. The third transistor 84 has its base terminal connected tothe collector terminal of the first transistor 82 and the resistor 88and its collector terminal is connected to the black area controlresistor 89. Note that each of the first transistor 82, the secondtransistor 83 and the third transistor 84 is operated to become ON/OFFaccording to the potential difference between the base and the emitterthereof.

The resistor 88 has one of its ends connected to the collector terminalof the first transistor 82 and the base terminal of the third transistor84 in order to regulate the voltage applied from the first transistor 82to the third transistor 84. The black area control resistor 89 has oneof its ends connected to the base terminal of the second transistor 83and its other end connected to the collector terminal of the thirdtransistor 84 in order to limit the electric current supplied from thesecond current source 93 and the capacitor 90 to the third transistor84. The capacitor 90 typically stores an electric charge thatcorresponds to the current value of the black peak and is connected tothe connection point of the above-described second transistor 83 and theblack area control resistor 89 as well as to the output section 91 andthe second current source 93.

Now, the operation of the black peak holding section 74 will bedescribed below.

The first transistor 82 and the second transistor 83 form an operationalamplifier for switching operations. The first transistor 82 becomes ONand the second transistor 83 becomes OFF when the base potential of thefirst transistor 82 is lower than the base potential of the secondtransistor 83, whereas the first transistor 82 becomes OFF and thesecond transistor 83 becomes ON when the base potential of the firsttransistor 82 is higher than the base potential of the second transistor83.

When a video signal showing a black peak level lower than the currentlyheld black peak level is input to the black peak holding section 74having such an operational amplifier by way of the input section 81, thebase potential of the first transistor 82 is lowered to make the firsttransistor 82 become ON. As a result, an electric current flows from thecollector terminal of the first transistor 82 to the resistor 88 toraise the potential difference between the opposite ends of the resistor88.

As the potential difference between the opposite ends of the resistor 88rises to such an extent as to turn on the third transistor 84, thetransistor 84 becomes ON and an electric current flows from the secondcurrent source 93 and the capacitor 90 to the third transistor by way ofthe collector terminal thereof. As a result, the base potential of thesecond transistor 83 is lowered. In other words, when a video signalwhose black peak level is lower than the black peak level that iscurrently held by the black peak holding section 74 is input, the blackpeak holding section 74 lowers the black peak level it holds to thelower black peak level.

When, on the other hand, a video signal showing a black peak levelhigher than the currently held black peak level is input to the blackpeak holding section 74 by way of the input section 81, the basepotential of the first transistor 82 is raised to make the secondtransistor 83 become ON. As a result, the first transistor 82 becomesOFF and hence the third transistor 84 also becomes OFF so that theelectric current output from the second current source 93 is stored inthe capacitor 90.

Thus, as the above sequence of operation is repeated, the lowest levelof the input video signal, or the black peak level, is held to the baseterminal of the second transistor 83.

FIG. 4 illustrates the relationship between the input video signal E andthe black peak level BL held by the black peak holding section 74. InFIG. 4, dotted line Bp1 indicates the black peak level when the blackarea control resistor 89 is ignored. If point a₁₁ in FIG. 4 shows thevoltage currently held for the black peak and an input signal having alower value is entered, the black peak holding level falls to point a₁₂and a new black peak is held. If the voltage of the input signal risesfrom there, the third transistor 84 in FIG. 3 becomes OFF and theelectric current from the second current source 93 is stored in thecapacitor 90. Since the current value from the second current source 93is typically very small, the voltage of the output gradually rises. Inthis way, the black peak holding operation proceeds.

In FIG. 4, dotted line Bp2 indicates the black peak level when the blackarea control resistor 89 is made to show a large resistance. Since theelectric current supplied to the third transistor 84 is limited by theblack area control resistor 89, the capability of tracking the blackpeak holding level in response to the input signal falls so that theblack peak holding level rises if compared with the dotted line Bp1 .

In other words, the black peak level that is held changes as a functionof the resistance of the black area control resistor 89. For the blackpeak level indicated by the dotted line Bp2 falls to the black peaklevel indicated by the dotted line Bp1, the black area of the inputsignal needs to be greater. Differently stated, it is possible for theblack peak holding section 74 of the video signal-processing device 7 todetermine the area of a black region for which an operation of blackexpansion is conducted by means of the black area control resistor 89 byselecting the resistance of the black area control resistor 89.

With the above described known video signal-processing device 7, theblack peak level held by the black peak holding section 74 theoreticallyundulates as shown by the dotted lines Bp1 and Bp2 in FIG. 4 so that, ifblack is expanded according to the black peak holding level, the imagebeing displayed may show mainly vertical shading depending on the videosignal, which is visually not pleasant to the viewers.

While the undulations of the black peak holding level can be reduced byincreasing the capacitance of the capacitor 90 and/or reducing theelectric current supplied from the second current source 93, therearises a problem that the known video signal-processing device 7 cannotrespond sufficiently quickly when a video signal for a quickly changingscene is input.

Furthermore, when an analog system is used and the component blocks ofthe black peak holding section 74 shown in FIG. 3 are realized by usingICs, there arises a problem that the current values of the black areacontrol resistor 89, the capacitor 90 and the first and second currentsources 92, 93 can disperse to make it difficult for the videosignal-processing device 7 to operate stably.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a noveldevice and a novel method for processing video signals that can dissolvethe above identified problems of known video signal-processing devices.

Another object of the present invention is to provide a device and amethod for processing video signals that can improve the resolution oftelevision receiving sets by accurately expanding black.

The above objects and other objects of the invention are achievedproviding a device and a method for processing video signals that areadapted to accurately expand black when the luminance component of theinput video signal is not higher than a first luminance level byregulating the computationally determined extent of black expansion onthe basis of the luminance component of the output video signal that isnot higher than a second luminance level integrated for one field inorder to improve the apparent contrast of the luminance signal at thetelevision receiving set.

A video signal-processing device according to the invention comprises aquantity of black expansion computing section for computationallydetermining the quantity of black expansion when the luminance componentof the input video signal is not higher than a first luminance level, aregulating means for regulating the quantity of black expansioncomputationally determined by the quantity of black expansion computingsection, an output video signal generating means for generating anoutput video signal by adding the quantity of black expansion regulatedby the regulating means to the luminance component of the input videosignal and a first field integrating means for integrating the luminancecomponent of the output video signal not higher than a second luminancelevel for a field. The regulating means of the processing deviceregulates the quantity of black expansion according to the luminancecomponent integrated by the first field integrating means.

A video signal-processing method according to the invention comprisescomputationally determining the quantity of black expansion when theluminance component of the input video signal is not higher than a firstluminance level, regulating the computationally determined quantity ofblack expansion, generating an output video signal by adding theregulated quantity of black expansion to the luminance component of theinput video signal, integrating the luminance component of the outputvideo signal not higher than a second luminance level for a field andfurther regulating the quantity of black expansion according to theintegrated luminance component.

Still other objects and specific advantages of the present inventionwill become apparent from the following description of preferredembodiments given below by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block circuit diagram of a known videosignal-processing device;

FIGS. 2A and 2B are graphs illustrating black expansion of a known videosignal-processing device;

FIG. 3 is a schematic circuit diagram of the black peak holding sectionof a known video signal-processing device;

FIG. 4 is a graph illustrating the relationship between an input videosignal and the black peak level held by the black peak holding section;

FIG. 5 is a schematic block circuit diagram of video signal-processingdevice according to the invention;

FIG. 6 is a graph schematically illustrating the difference by thedifference computing section;

FIG. 7 is a graph schematically illustrating the quantity of blackexpansion computed by the quantity of black expansion computing section;

FIGS. 8A and 8B are graphs schematically illustrating the luminancecomponent of the output video signal generated by adding the quantity ofblack expansion to the luminance component of the input video signal bythe quantity of black expansion computing section;

FIG. 9 is a schematic block diagram of the gain computing block;

FIG. 10 is a graph schematically illustrating an operation of computingthe black area;

FIG. 11 is a graph schematically illustrating an operation of selectinga pedestal level; and

FIG. 12 is a graph schematically illustrating an operation of comparingthe modified integrated quantity of the convergence check section.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, a device and a method for processing video signals according to thepresent invention will be described in detail by referring to theaccompanying drawings.

As shown in FIG. 5, a video signal-processing device 1 according to theinvention comprises an input terminal 11 for receiving input videosignals from broadcasting stations, a difference computing section 12, aquantity of black expansion computing section 13, a black expansionlevel output section 14, a gain controller 15, a quantity of blackexpansion adding section 16, a gain determining block 17 and an outputterminal 18 for outputting the output video signal to a televisionreceiving set. The video signal-processing device 1 distinguishes theluminance signal of the input video signal depending on the contents ofthe signal and, if necessary, expands black to the pedestal level, whichis the reference level for black, for the purpose of convergence.

The difference computing section 12 receives the input video signaltransmitted from the input terminal 11 and also the black expansionlevel for starting an operation of black expansion transmitted from theblack expansion level output section 14. The difference computingsection 12 obtains the difference between the luminance component of theinput video signal and black expansion level, and outputs it to thequantity of black expansion computing section 13.

The quantity of black expansion computing section 13 receives thedifference between the luminance component of the input video signal andthe black expansion level. The quantity of black expansion computingsection 13 computes the quantity of black expansion depending on thedifference and outputs it to the gain controller 15.

The gain controller 15 regulates the quantity of black expansion inputfrom the quantity of black expansion computing section 13 on the basisof the feedback gain supplied from the gain determining block 17. Thegain controller 15 realizes the above described operation of regulatingthe quantity of black expansion by multiplying the quantity of blackexpansion typically by the supplied feedback gain. The gain controller15 may perform the above described operation of regulating the quantityof black expansion on a field by field basis. The gain controller 15transmits the regulated quantity of black expansion to the quantity ofblack expansion adding section 16.

The quantity of black expansion adding section 16 receives the inputvideo signal transmitted from the input terminal 11 and the quantity ofblack expansion from the gain controller 15. Then, the quantity of blackexpansion adding section 16 generates an output video signal by addingthe quantity of black expansion to the luminance component of the inputvideo signal and transmits it to the gain determining block 17 and theoutput terminal 18. Note that the luminance component of the outputvideo signal is expanded to the black side because the quantity of blackexpansion with a negative polarity is added to the luminance componentof the input video signal with a positive polarity.

The gain determining block 17 distinguishes the luminance signalcomponent of the output video signal supplied from the quantity of blackexpansion adding section 16, computationally determines the feedbackgain of black expansion and supplies it to the gain controller 15.

The feedback gain generated by the gain determining block 17 may bedefined to be not smaller than 0 and not greater than 1. The quantity ofblack expansion can be transmitted to the quantity of black expansionadding section 16 without modification if 1 is selected for the feedbackgain, whereas the operation of black expansion can be suspended if 0 isselected for the feedback gain. The gain determining block 17 will bedescribed in greater detail hereinafter.

The output terminal 18 outputs the output video signal supplied from thequantity of black expansion adding section 16 to the televisionreceiving set (not shown).

Now, a typical operation of the video signal-processing device 1 will bedescribed below.

The difference computing section 12 determines the difference betweenthe luminance component of the input video signal transmitted from theinput terminal 11 and the black expansion level. If the luminancecomponent Yc of the input video signal indicated by the solid obliqueline in FIG. 6 is equal to the black expansion level Bp, the differenceDf indicated by the horizontal axis is equal to 0. The difference Dfindicated by the horizontal axis increases as the luminance component Ysof the input video signal downwardly leaves the black expansion levelBp. If the luminance component Ys of the input video signal is greaterthan the black expansion level Bp, the luminance of the video signal isprevented from falling at the white side by selecting 0 for thedifference.

The quantity of black expansion computing section 13 may so compute thequantity of black expansion as to bring the difference to square asshown in FIG. 7 in order to increase the quantity of black expansion Bpremarkably as the computed difference Df increases. Then, the quantityof black expansion computing section 13 transmits the computed quantityof black expansion to the gain controller 15.

The gain controller 15 regulates the quantity of black expansion bymultiplying the quantity of black expansion computed in a manner asdescribed above by the feedback gain transmitted from the gaindetermining block 17 and transmits the regulated quantity of blackexpansion to the quantity of black expansion adding section 16.

The quantity of black expansion adding section 16 generates an outputvideo signal on the basis of the quantity of black expansion regulatedby the gain controller 15. FIGS. 8A and 8B are graphs showing theluminance component Yb of the output video signal generated by addingthe above described quantity of black expansion with a negative polarityto the luminance component Yc of the input video signal. As shown inFIGS. 8A and 8B, the quantity of black expansion is made equal to 0 whenthe luminance component Yc of the input video signal is not smaller thanthe black expansion level Bp so that the luminance component Yb of theoutput video signal agrees with the luminance component Yc of the inputvideo signal. On the other hand, the quantity of black expansionincreases as the luminance component Yc of the input video signal fallsbelow the black expansion level Bp so that consequently the luminancecomponent Yb of the output video signal is reduced.

The feedback gain supplied from the gain determining block 17 is addedto the quantity of black expansion as described above. FIG. 8A shows aninstance where the quantity of black expansion is multiplied by thefeedback gain that is equal to 1. The quantity of black expansionincreases and the luminance component Yb of the output video signalexceeds the pedestal level as the luminance component Yc of the inputvideo signal falls far below the black expansion level Bp. Therefore,when the luminance component Yb of the output video signal falls belowthe pedestal level, the quantity of black expansion is suppressed toconverge the luminance component Yb of the output video signal to thepedestal level by making the feedback gain smaller than 1 as shown inFIG. 8B.

The video signal-processing device 1 of this embodiment extracts theinput video signal by way of the difference computing section 12 and theblack expansion level output section 14 as the input video signal issequentially supplied by way of the input terminal 11, and computes thequantity of black expansion only when the video signal is determined asa signal showing a level that needs to be expanded. The videosignal-processing device 1 generates the output video signal to besupplied to the television receiving set by feeding back the computedquantity of black expansion by way of the gain determining block 17 in acontrolled manner and sequentially adding it to the input video signal.With this arrangement, the video signal that is recognized as signalshowing a black level that needs to be expanded is subjected to blackexpansion and the feedback gain is made smaller than 1 to suppress thequantity of black expansion and converge the luminance component of theoutput video signal to the pedestal level when the level falls below thepedestal level as a result of expansion. Thus, it is possible to improvethe apparent contrast.

The configuration of the gain determining block 17 will be describedbelow by referring to FIG. 9.

The gain determining block 17 comprises an LPF 19, a horizontal spancomputing block 20, a vertical span adding block 29, a black areadetecting section 36, a third multiplier 37, a fourth multiplier 38, asecond scaling section 39, a limiter 41, a limit value generatingsection 42, an area scaling section 43, a fifth multiplier 44, aconvergence checking section 45, a convergence level determining section46, a processing section 50, a third adder 55, a latch section 56 and apulse generating section 57.

The LPF 19 removes noises from the output video signal that is suppliedfrom the quantity of black expansion adding section 16 in order toprevent the noises generated during the process of signaltransmission/reception from being recognized as video signal to besubjected to black expansion and transmits the output video signal tothe horizontal span computing block 20.

The horizontal span computing block 20 has a first adder 22, an SLEVHoutput section 23, a first horizontal span adding section 24, a secondadder 25, an SLEVL output section 26, a second horizontal span addingsection 27 and a first masking signal generating section 28.

The first adder 22 carriers out a subtraction on the input signal on thebasis of the signal supplied from the SLEVH output section 23 andoutputs the outcome of the subtraction to the first horizontal spanadding section 24. The first horizontal span adding section 24 adds theinput signals for a horizontal line in each and every dot clock andoutputs the outcome of the addition to the vertical span adding block29.

The second adder 25 carries out a subtraction on the input signal on thebasis of the signal supplied from the SLEVL output section 26 andoutputs the outcome of the subtraction to the second horizontal spanadding section 27. The second horizontal span adding section 27 adds theinput signals for a horizontal line in each and every dot clock andoutputs the outcome of the addition to the vertical span adding block29.

The first masking signal generating section 28 removes the synchronizingsignal and other elements by transmitting a masking signal to the firsthorizontal span adding section 24 and the second horizontal span addingsection 27.

The vertical span adding block 29 has a first scaling section 30, afirst multiplier 31, a second multiplier 32, a first vertical spanadding section 33, a second vertical span adding section 34 and a secondmasking signal generating section 35.

The first multiplier 31 and the second multiplier 32 scales the signalsreceived from the horizontal span adding sections 24 and 27 on the basisof the scaling factor input from the first scaling section 30.

The first vertical span adding section 33 further integrates the signalreceived from the first multiplier 31 for a field in a verticaldirection on a line by line basis. The second vertical span addingsection 34 further integrates the signal received from the secondmultiplier 32 for a field in a vertical direction on a line by linebasis.

The second masking signal generating section 35 removes thesynchronizing signal and other elements by transmitting a masking signalto the first vertical span adding section 33 and the second verticalspan adding section 34.

The black area detecting section 36 determines the difference betweenthe signal input from the first vertical span adding section 33 and thesignal input from the second vertical span adding section 34 andtransmits it to the fourth multiplier. The third multiplier 37 scalesthe signal received from the first vertical span adding section 33 onthe basis of the scaling factor input from the second scaling section 39and outputs the result to the third multiplier 37. The fourth multiplier38 scales the signal received from the black area detecting section 36on the basis of the scaling factor input from the scaling section 39 andoutputs the result to the limiter 41.

The limiter 41 imposes a limit on the signal received from the fourthmultiplier 38 on the basis of the limiter signal received from the limitvalue generating section 42 and transmits the obtained signal to thearea scaling section 43. The area scaling section 43 performs an areascaling operation, which will be described in greater detailhereinafter, on the signal input from the limiter 41 and outputs theobtained signal to the fifth multiplier 44. The fifth multiplier 44multiplies the signals input from the third multiplier 37 and the areascaling section 43 and transmits the outcome to the convergence checkingsection 45.

The convergence checking section 45 compares the signal level of thesignal input from the convergence level determining section 46 and thesignal level of the signal received from the fifth multiplier 44 andtransmits the result of comparison to the processing section 50.

The processing section 50 includes processing circuits 51 through 53 andis adapted to generate difference feedback gain that corresponds to theresult of comparison received from the convergence checking section 45.

The third adding section 55 receives the difference feedback gain fromthe processing section 50 and also receives the feedback gain of theimmediately preceding field from the latch section 56. The third addingsection 55 then adds the difference feedback gain and the feedback gainof the immediately preceding field to obtain the feedback gain of thecurrent field.

The latch section 56 stores the feedback gain of the current fieldgenerated by the third adding section 55 on the basis of the pulsetransmitted from the pulse generating section 57 and supplies thefeedback gain to the gain controller 15. The latch section 56 can supplyfeedback gains to the gain controller 15 on a field by field basis as itstores the feedback gain for each and every field.

The pulse generating section 57 oscillates to generate a pulse for thelatch section 56 at predetermined timings in order to prevent thefeedback gain from fluctuating in a same field.

Now, a typical operation of the gain determining block 17 will bedescribed below.

Firstly, the LPF 19 removes noises from the output video signal outputfrom the quantity of black expansion adding section 16. As a result, thenoises generated during the process of signal transmission/reception areprevented from being recognized as video signal that needs to besubjected to an operation of black expansion. The LPF 19 then transmitsthe output video signal to the horizontal span computing block 20.

The first adder 22 receives an SLEVH signal suggesting that the outputvideo signal that is subjected to an operation of black expansion isapproaching the pedestal level from the SLEVH output section 23 and alsoreceives the output video signal from the LPF 19. Assume here that thesignal level of the SLEVH signal is not lower than the pedestal leveland not higher than the black expansion level. The first adder 22subtracts the luminance component of the output video signal and theSLEVH signal and generates differential added luminance level A1, whichis then transmitted to the first horizontal span adding section 24.

The first horizontal span adding section 24 adds the differential addedluminance levels Al received from the first adder 22 for a horizontalline in each and every dot clock and transmits the outcome of theaddition to the first multiplier 31 of the vertical span adding block 29as horizontally added luminance level A2. In other words, the luminancecomponent of the output video signal that is not higher than the signallevel of the SLEVH signal is integrated for a horizontal line for thehorizontally added luminance level A2.

The second adder 25 receives the SLEVL signal whose level is selected soas to be lower than the level of the above described SLEVH signal fromthe SLEVL output section 26 and also the output video signal from theLPF 19. The second adder 25 then adds the luminance component of theoutput video signal and the SLEVL signal to generate a differentialadded luminance level B1 and transmits it to the second horizontal spanadding section 27.

The second horizontal span adding section 27 adds the differential addedluminance levels B1 received from the second adder 25 for a horizontalline in each and every dot clock and transmits the result to the secondmultiplier 32 of the vertical span adding block 29 as horizontally addedluminance level B2. In other words, the luminance component of theoutput video signal that is not higher than the signal level of theSLEVL signal is integrated for a horizontal line for the horizontallyadded luminance level B2.

The first masking signal generating section 28 prevents any additionfrom taking place in the horizontal synchronizing signal span that isintrinsically not an effective viewing range by transmitting a maskingsignal to the first horizontal span adding section 24 and the secondhorizontal span adding section 27.

The first multiplier 31 receives the horizontally added luminance levelA2 obtained by the addition in the horizontal direction from the firsthorizontal span adding section 24 and also receives the scaling factorform the first scaling section 30. The first multiplier 31 can detectrelatively same differential added luminance levels for various formatswith different numbers of horizontal dots by multiplying thehorizontally added luminance level A2 by the scaling factor.

Similarly, the second multiplier 32 receives the horizontally addedluminance level B2 from the second horizontal span adding section 27 andalso receives the scaling factor form the first scaling section 30. Thesecond multiplier 32 performs a scaling operation by multiplying thehorizontally added luminance level B2 by the scaling factor.

The first vertical span adding section 33 further integrates thehorizontally added luminance level A2 received from the first multiplier31 for a field in a vertical direction on a line by line basis. As aresult, it is possible to integrate the luminance component of theoutput video signal that is not higher than the signal level of theSLEVH signal for a field. The luminance component integrated for a fieldby the first vertical span adding section 33 is referred to as fieldintegration quantity A3 hereinafter.

The second vertical span adding section 34 further integrates thehorizontally added luminance level B2 received from the secondmultiplier 32 for a field in a vertical direction on a line by linebasis. As a result, it is possible to integrate the luminance componentof the output video signal that is not higher than the signal level ofthe SLEVL signal for a field. The luminance component integrated for afield by the second vertical span adding section 34 is referred to asfield integration quantity B3 hereinafter.

The second masking signal generating section 35 transmits a maskingsignal to the first vertical span adding section 33 and the secondvertical span adding section 34. In this operation, any addition isprevented from taking place in the vertical synchronizing signal spanthat is intrinsically not an effective viewing range.

Since a higher signal level is selected for a SLEVH signal than for theSLEVL signal, the field integration quantity A3 is greater than thefield integration quantity B3. The field integration quantities A3, B3are transmitted to the black area detecting section 36. The fieldintegration quantity A3 is also transmitted to the third multiplier 37.

The black area detecting section 36 receives the field integrationquantity A3 and the field integration quantity B3. The black areadetecting section 36 determines the area of the pixels having aluminance component that is not higher than the SLEVH signal in a fieldby determining the difference of the field integration quantity A3 andthe field integration quantity B3. The area of the pixels having aluminance component that is not higher than the SLEVH signal is referredto as black area hereinafter. Information on the black area is referredto as black area information hereinafter. FIG. 10 is a graphschematically illustrating an operation of computing the black area.Referring to FIG. 10, the difference between the field integrationquantity A3 and the field integration quantity B3 becomes equal to thearea of the pixels having a luminance component that is not higher thanthe SLEVH signal in the field by making the difference of luminance Ysbetween the SLEVH signal and the SLEVL signal equal to 1.

The third multiplier 37 scales the field integration quantity A3received from the first vertical span adding section 33, using thescaling factor input from the second scaling section 39 and outputs theobtained result to the fifth multiplier 44. The fourth multiplier 38scales the received black area information, using the scaling factorinput from the second scaling section 39 and transmits the obtainedresult to the limiter 41.

The limiter 41 receives the black area information from the fourthmultiplier 38. The limiter 41 generates a limit value for limiting theblack area contained in the black area information by means of the limitvalue generating section 42. The limiter 41 prevents an overflowingphenomenon from taking place in the area computing operation of the areascaling section 43, which is located downstream, by limiting the blackarea contained in the black area information on the basis of the limitvalue or transmission of black area information on black area 0 to thearea scaling section 43 from taking place. The limiter 41 can preventthe area scaling section 43, which is located downstream, from scalingthe slight black area that exists in the field in order to suppressdegradation of the image quality by limiting the black area contained inthe black area information.

The area scaling section 43 extracts the black area from the black areainformation input from the limiter 41 and scales it. The area scalingsection 43 scales the black area on the basis of the ratio to themaximum value of the black area in the current field. In the followingdescription, when a field is totally occupied by a black area, the areais referred to as flat field. If the extracted black area is X and theflat field is A, the area scaling section 43 computes A/X for thescaling operation. The value of A/X as computed by the area scalingsection 43 indicates the ratio of the black area to the flat field.

The fifth multiplier 44 receives the field integration quantity A3 fromthe third multiplier 37 and the value of A/X from the area scalingsection 43. The fifth multiplier 44 multiplies the field integrationquantity A3 by A/X to generate modified integrated quantity A4 andtransmits it to the convergence checking section 45. As a result of themultiplication by the fifth multiplier 44, using A/X, the field can beapparently treated as flat field if the black area distributed in thefield can show dispersion to further improve the characteristicsrelative to the visual sense. The fifth multiplier 44 transmits themodified integration quantity A4 that is obtained as a result of thearea scaling to the downstream convergence checking section 45. Then,the convergence checking section 45 can judge the extent of convergenceby taking the ratio of the black area in the current field intoconsideration.

The convergence level determining section 46 stores in advance theconverged integrated quantity A0 obtained by integrating the differencebetween the pedestal level L₁ and the signal level of the SLEVH signalfor a field. Note that the median value of SUMMAX and SLEVH may beselected for the pedestal level L₁, where SUMMAX is the detectableminimum value of modified integration quantity A4 as illustrated in FIG.11. Also note that the convergence level determining section 46 mayalternatively compute the converged integrated quantity A0 on the basisof an upper convergence level L₂ and a lower convergence level L₃selected so as to sandwich the pedestal level L₁ instead of the pedestallevel L₁ as shown in FIG. 11.

The convergence checking section 45 receives the modified integratedquantity A4 from the fifth multiplier 44 and the converged integratedquantity A0 from the convergence level determining section 46. Theconvergence checking section 45 compares the modified integratedquantity A4 and the converged integrated quantity A0 typically bydetermining the difference between them as shown in FIG. 12 andtransmits the result of comparison to the processing section 50.

The processing section 50 includes processing circuits 51 through 53 andis adapted to generate differential feedback gains C1, C2, C3 as afunction of the result of comparison received from the convergencechecking section 45.

If the modified integrated quantity A4 is smaller than the convergedintegrated quantity A0, the processing section 50 generates differentialfeedback gain C1 that is used to raise the feedback gain Fc by way ofthe processing circuit 51. The processing circuit 51 computes modifiedintegrated quantity A4—converged integrated quantity A0| and multipliesit by the positive polarity transmitted from HLD transmitting section 51b in the multiplication circuit 51 a to generate differential feedbackgain C1 so as to raise the feedback gain it generates to a large extentwhen the difference between the modified integrated quantity A4 and theconvergence level is large.

When the modified integrated quantity A4 is larger than the convergedintegrated quantity A0, the processing section 50 generates differentialfeedback gain C2 in order to lower the feedback gain by way of theprocessing circuit 52. The processing circuit 52 computes |modifiedintegrated quantity A4—converged integrated quantity A0| and multipliesit by the negative polarity transmitted from ATK transmitting section 52b in the multiplication circuit 52 a to generate differential feedbackgain C2 so as to raise the feedback gain it generates to a large extentwhen the difference between the modified integrated quantity A4 and theconvergence level is large.

If the received result of comparison tells that the modified integratedquantity A4 is equal to the converged integrated quantity A0, theprocessing section 50 judges that the quantity of black expansion isappropriate and the processing circuit 53 generates differentialfeedback gain C3 that is equal to “0” so as not to shift the feedbackgain.

If the convergence level determining section 46 is adapted to computethe converged integrated quantity A0 on the basis of an upperconvergence level L₂ and a lower convergence level L₃ instead of thepedestal level L₁, the processing section 50 generates differentialfeedback gain C3 when the modified integrated quantity A4 is foundbetween the two converged integrated quantities A0. With thisarrangement, ON and OFF are not repeated more frequently for blackexpansion to prevent images of black level from fluctuating and visualproblems from arising if compared with the arrangement where theconverged integrated quantity is computed on the basis of the pedestallevel.

The processing section 50 transmits the differential feedback gains C1,C2, C3 it generates to the third adding section 55.

The third adding section 55 receives the differential feedback gains C1,C2, C3 from the processing section 50 and the feedback gain Fc of theimmediately preceding field from the latch section 56. The third addingsection 55 then adds the differential feedback gains and the feedbackgain FC of the immediately preceding field to use the sum as thefeedback gain Fc of the current field. As a result of generating such afeedback gain Fc, black expansion is promoted when the modifiedintegrated quantity A4 is smaller than the converged integrated quantityA0, whereas it is suspended when the modified integrated quantity A4exceeds the converged integrated quantity A0.

As a result of storing the feedback gain of the current field by way ofthe latch section 56, it is possible to prevent the feedback gain to besupplied to the gain controller 15 from fluctuating in a same field sothat the feedback gain would no longer be shifted while an image isbeing displayed on the television receiving set. Thus, the phenomenon ofpseudo-profile and that of shading can be prevented from appearing ifcompared with conventional video signal-processing devices adapted tohold the black peak.

As described above, the feedback gain that is transmitted to the gaincontroller 15 from the gain determining block 17 is generated byintegrating the luminance component of the output video signal that isnot higher than the signal level of the SLEVH signal for a field andcomparing the result of the integration with the converged integratedquantity obtained by integrating the difference between the pedestallevel and the signal level of the SLEVH signal for a field. With thisarrangement, it is possible to converge each detected black level to anoptimum luminance level on a field by field basis so that a videosignal-processing device according to the invention can respond quicklyeven when a video signal for quickly changing scenes is input andimprove the apparent contrast of the luminance component. Additionally,since the feedback gain can be generated by taking the ratio of theblack area into consideration, it is possible to improve the apparentcontrast of the luminance component for any input video signals withdifferent black areas.

According to the present invention, when the luminance component of theoutput video signal falls below SLEVH as shown in FIG. 8B, it ispossible to add a regulated quantity of black expansion on the basis ofthe feedback gain and hence it is possible to gradually bring theluminance component close to the pedestal level on a field by fieldbasis. Therefore, according to the invention, the quantity of blackexpansion can be reduced when the luminance component of the outputvideo signal that is subjected to black expansion falls below SLEVH,whereas the quantity of black expansion can be increased when theluminance component of the output video signal that is subjected toblack expansion rises above SLEVH. Therefore, it is possible to improvethe apparent contrast of the luminance component so as to be free fromlack of gradation for black.

Additionally, according to the invention, since the internal resistancesof the ICs and the capacitances of capacitors are free from variancesunlike known video processing devices, it is possible to accuratelycompute the black area and the modified integrated quantity A4. As aresult, black expansions can be realized highly accurately to eliminatecomparison motions due to undulations that are observed with the peakholding system and hence it is possible to stabilize the black levelbecause the black level is processed for black expansion in order tohold the feedback gain to a constant level in each field.

The present invention is by no means limited to the above embodimentsthat are described by referring to the accompanying drawings, whichembodiments may be modified and altered in various different wayswithout departing from the scope of the invention as may be apparent tothose who are skilled in the art.

Industrial Applicability

As has been described above, according to the present invention, thedevice and the method for processing video signals regulates thecomputed quantity of black expansion on the basis of the luminancecomponent of the output video signal that is not higher than the signallevel of the SLEVH signal integrated for a field, when the luminancecomponent of the input video signal is not higher than the blackexpansion level. Since the feedback gain can be generated by taking theratio of the black area into consideration, it is possible to improvethe apparent contrast of the luminance component in the televisionreceiving set for any input video signals with difference black areas.

1. a video signal-processing device comprising: quantity of blackexpansion computing means for computationally determining a quantity ofblack expansion when a luminance component of an input video signal isnot higher than a first luminance level; regulating means for regulatingthe quantity of black expansion computationally determined by thequantity of black expansion computing means; output video signalgenerating means for generating an output video signal by adding thequantity of black expansion regulated by the regulating means to theluminance component of the input video signal; and field integratingmeans for integrating the luminance component of the output video signalnot higher than a second luminance level for a field of the input videosignal, wherein the regulating means is adapted to regulate the quantityof black expansion according to the luminance component integrated bythe field integrating means.
 2. The device according to claim 1, whereinthe quantity of black expansion computing means computes the quantity ofblack expansion according to a difference between the luminancecomponent of the input video signal and the first luminance level. 3.The device according to claim 1, further comprising: comparing means forcomparing the luminance component as integrated by the field integratingmeans with a predefined convergence level; wherein the regulating meansis adapted to regulate the quantity of black expansion according to aresult of comparison of the comparing means.
 4. The device according toclaim 3, wherein the regulating means is adapted to increase thequantity of black expansion when the integrated luminance component issmaller than the predefined convergence level, to limit the quantity ofblack expansion when the integrated luminance component is larger thanthe convergence level, and to make the quantity of black expansion equalto 0 when the integrated luminance component is equal to the predefinedconvergence level.
 5. The device according to claim 3, wherein theregulating means regulates the quantity of black expansion based on adifference between the integrated luminance component and the predefinedconvergence level.
 6. The device according to claim 3, wherein thecomparing means makes the quantity of black expansion equal to 0 whenthe integrated luminance component is close to the predefinedconvergence level.
 7. The device according to claim 3, furthercomprising: gain output means for outputting a feedback gain accordingto the result of the comparison as transmitted from of the comparingmeans, wherein the regulating means is adapted to regulate the quantityof black expansion by multiplying the quantity of black expansion by thefeedback gain output from the gain output means.
 8. The device accordingto claim 1, further comprising: black area computing means for computinga black area where the luminance component is not higher than the secondluminance level in the field of the output video signal, wherein theregulating means being is adapted to regulate the quantity of blackexpansion based on the basis of the luminance component integrated bythe first field integrating means and the black area determined by theblack area computing means.
 9. The device according to claim 8, whereinthe field integrating means comprises first field integrating means andfurther comprising: second field integrating means for integrating theluminance component of the output video signal not higher than a thirdluminance level for a field of the input video signal, wherein the blackarea computing means is adapted to determine the black area according toa difference between the output of the first field integrating means andthe output of the second field integrating means.
 10. The deviceaccording to claim 1, wherein the regulating means is adapted toregulate the quantity of black expansion on a field by field basis. 11.A video signal-processing method comprising the steps of:computationally determining a quantity of black expansion when aluminance component of an input video signal is not higher than a firstluminance level; regulating the computationally determined quantity ofblack expansion; generating an output video signal by adding theregulated quantity of black expansion to the luminance component of theinput video signal; integrating the luminance component of the outputvideo signal not higher than a second luminance level for a field of theinput video signal; and further regulating the quantity of blackexpansion according to the integrated luminance component.
 12. Themethod according to claim 11, wherein the quantity of black expansion iscomputed according to a difference between the luminance component ofthe input video signal and the first luminance level.
 13. The methodaccording to claim 11, further comprising the step of: comparing theintegrated luminance component with a predefined convergence level so asto regulate the quantity of black expansion according to a result ofcomparison of the step of comparing means.
 14. The method according toclaim 13, further comprising the steps of: increasing the quantity ofblack expansion when the integrated luminance component is smaller thanthe convergence level; and limiting the quantity of black expansion whenthe integrated luminance component is larger than the convergence level,wherein the quantity of black expansion is made equal to 0 when theintegrated luminance component is equal to the convergence level. 15.method according to claim 13, further comprising the step of regulatingthe quantity of black expansion based on a difference between theintegrated luminance component and the convergence level.
 16. The methodaccording to claim 13, further comprising the step of regulating thequantity of black expansion to be equal to 0 when the integratedluminance component is close to the convergence level.
 17. The methodaccording to claim 13, further comprising the step of: generating afeedback gain according to the result of the comparison in the comparingstep, wherein the quantity of black expansion is regulated bymultiplying the quantity of black expansion by the generated feedbackgain.
 18. The method according to claim 11, further comprising the stepof: computing a black area where the luminance component is not higherthan the second luminance level in the field of the output video signal,wherein the quantity of black expansion being is regulated based on thebasis of the integrated luminance component and the determined blackarea.
 19. The method according to claim 18, further comprising the stepof: integrating the luminance component of the output video signal nothigher than a third luminance level for a field, wherein the black areabeing is determined based on a difference between the integratedluminance component and the luminance component obtained by integratingthe output video signal not higher than the second luminance level for afield.
 20. The method according to claim 11, wherein the quantity ofblack expansion is regulated on a field by field basis.